US3740488A - Inductive loop through-the-earth communication system - Google Patents

Inductive loop through-the-earth communication system Download PDF

Info

Publication number
US3740488A
US3740488A US00106034A US3740488DA US3740488A US 3740488 A US3740488 A US 3740488A US 00106034 A US00106034 A US 00106034A US 3740488D A US3740488D A US 3740488DA US 3740488 A US3740488 A US 3740488A
Authority
US
United States
Prior art keywords
antenna
audio
amplifier
earth
secondary winding
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US00106034A
Other languages
English (en)
Inventor
R Linfield
A Farstad
J Allen
L Ball
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
CBS Corp
Original Assignee
Westinghouse Electric Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Westinghouse Electric Corp filed Critical Westinghouse Electric Corp
Application granted granted Critical
Publication of US3740488A publication Critical patent/US3740488A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B5/00—Near-field transmission systems, e.g. inductive or capacitive transmission systems
    • H04B5/20—Near-field transmission systems, e.g. inductive or capacitive transmission systems characterised by the transmission technique; characterised by the transmission medium
    • H04B5/24—Inductive coupling
    • H04B5/26—Inductive coupling using coils
    • H04B5/266—One coil at each side, e.g. with primary and secondary coils

Definitions

  • SHEET 2 BF 5 I VOICE BAND-+ I60 I l
  • FIG. l2 PREAMP p w PATENIED JUM 9 I975 SHEET 5 OF 5 FIG. I5
  • the invention generally relates to communication systems, and particularly to a through the earth voice communication system.
  • injured and uninjured men will leave the vicinity of the explosion and fires, and will seek refuge in pre-existing refuge chambers at various locations within the mine. Smaller groups of men may be trapped anywhere within the mine and may not have access to these refuge chambers or other special equipment previously placed in designated areas. These men will likely have no equipment or means of communication other than that which was part of their attire at the time of the disaster.
  • a carrier signal is modulated by the voice intelligence to be transmitted, such modulation being in the form of frequency modulation, amplitude modulation or pulse position modulation, for example.
  • the higher frequencies are attenuated more and accordingly the carrier signal is attenuated after a relatively short distance through the earth.
  • the carrier signal is attenuated after a relatively short distance through the earth.
  • much more expensive and higher powered transmitting equipment is required to compensate for the attenuation.
  • the present invention provides a through the earth voice communication system which allows for great separation between transmitter and receiver, and wherein the receiver may be carried on a person, and wherein voice reproduction is of extremely high quality.
  • a transmitter means for transmitting an audio signal through the earth to a receiver.
  • the signal transmitted is a band of frequencies within the audio range.
  • the transmitter and receiver may be at the same, or different levels with one, or both being located within the earth.
  • the receiver means includes an audio amplifier, a loop antenna coupled to the audio amplifier and an output, such as a speaker or earphone for converting the audio amplifier output to an audible sig- BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 illustrates, with portions broken away, a mine environment in which the present invention may be utilized;
  • FIG. 2 is a block diagram of the transmitter means
  • FIG. 3 is a block diagram of the receiver means
  • FIG. 4 is a curve illustrating the attenuation of various frequencies in through the earth transmission
  • FIG. 5 is a curve illustrating the loop antenna response
  • FIG. 6 is a curve illustrating the resultant signal obtained through the use of the loop antenna of FIG. 3, in conjunction with the transmitter means of FIG. 2;
  • FIG. 7 is a plan view
  • FIG. 8 is a side elevational view of the coverage obtained with a long line antenna
  • FIG. 9 is a block diagram illustrating a transmitter means for obtaining greater coverage
  • FIGS. 10 and 11 illustrate other antenna configurations
  • FIG. 12 illustrates another type of antenna which may be used in the transmitting means
  • FIG. 13 illustrates the invention in conjunction with a miners helmet
  • FIG. 14 illustrates another use for the present invention.
  • FIG. 15 is a curve illustrating the loop antenna response for the embodiment of FIG. 14.
  • FIG. 1 there is illustrated a mine site with a portion of the earth broken away to show a section of the mine 10.
  • a transmitter means 12 having a long line, insulated wire transmitting antenna 13 grounded at both ends 15 and 16 by connection to the earth.
  • the ends 15 and 16 may be grounded by a technique utilizing a plurality of grounding stakes driven into the ground in one or more groups with the stakes having, for example, salt water poured on them, and each being electrically connected to an end.
  • the transmitter means is operable to transmit an audio signal, directly and without modulating a carrier, through the earth to one or more receiver means.
  • a receiver means may be carried by each miner and will also be located in pre-existing refuge chambers 22.
  • the transmitter means 12 includes an audio frequency power amplifier for amplifying the audio signal provided by an input means such as microphone 27 in response to a speaker.
  • the audio amplifier can be driven with a preamplifier 29 of the type that is typically used for normal audio frequency amlification and a suitable power supply 31 is provided to supply necessary operating potentials.
  • the output of the audio frequency power amplifier 25 is an audio signal within the audio range.
  • the audio range occupies a band from approximately 20 to 20,000 HZ and speech occupies the band primarily. from 50 to 7,500 Hz although most of the information is contained within the 300 to 3,000 Hz range.
  • the transmitter means 12 may be designed to provide an output band of frequencies substantially within this lat-' ter range and herein termed the voice band.
  • a coupling and matching network in the form of a transformer 32 having a primary and secondary winding 33 and 34 respectively for matching the output of the amplifier 25 to the impedance of the antenna 13.
  • the transformer 32 may incorporate a secondary winding 34 which includes multiple taps 35 selectable, such as by a switch 36, to permit matching a wide variety of antenna impedances.
  • one section of antenna 13 may be coupled to one end of the transformer secondary winding and the other section of antenna 13 may be coupled to the switch 36.
  • the two antenna sections are preferably on respective reels carried by vehicles which may then drive off in opposite directions to antenna grounding positions. Alternatively one end may be grounded and a single long length of antenna wire, reel mounted and vehicle carried, may be connected to the switch (or vice versa).
  • the antenna should be buried just below the surface to avoid damage.
  • the receiving means 38 includes an audio amplifier designed for amplifying the band of frequencies being transmitted, and suitable filter means may be included for rejecting noise signals outside the transmitted band.
  • the audio amplifier 40 includes means for connection to a source of operating potential in a form of power supply 42. If the receiving apparatus is located within a refuge chamber, the power supply 42' may be a rechargeable battery within the chamber; if the receiving means 38 is carried by a miner, the power supply 42 may be from the battery normally carried by the miner to power his helmet carried light.
  • a receiving antenna in the form of loop antenna 46 is provided to receive the transmitted signal, and more particularly the magnetic field thereof, to provide an output voltage, herein termed the terminal voltage of the loop, to the audio amplifier.
  • the output of the audio amplifier 40 is connected to an output transducer means 49 for converting the output signal to an audible signal.
  • the output transducer means may, for example, be a speaker or a set of earphones.
  • FIG. 4 the horizontal axis is a log scale of frequency, and the vertical axis represents the strength of the magnetic field received, measured in decibels (db), relative to 1 amp per meter, a typical designation for magnetic field strength.
  • FIG. 4 illustrates the situation for a thousand foot depth with an earth conductivity of 10" mhos per meter.
  • Curve 52 is the resultant response with a transmitter antenna of a 1,000 meter length and a 1 ampere antenna current and curve 52', having a similar slope, is the response with an antenna of a meter length and a l ampere antenna current. It is seen that as the frequency increases, the magnetic field strength decreases and this is due to the fact that increased attenuation occurs with increased frequency. Since the field strength is not uniform across the voice band, any amplification thereof will result in a distorted and perhaps unintelligible output.
  • the loop antenna 46 is designated to compensate for this non-uniform attenuation.
  • the loop antenna 46 consists of winding 55 having a number of turns of wire disposed about a core which may be air, or for example, a ferrite core 57 as illustrated in FIG. 3.
  • a typical loop antenna response is illustrated in FIG. 5 wherein the horizontal axis is a log scale of frequency and the vertical axis represents the loop terminal voltage induced, due to a given magnetic field, the units being in decibels relative to one volt. Up until a point at which self resonance is approached, the induced RMS terminal voltage is given by the relationship:
  • V is in volts f is the frequency in hertz
  • A is the area of the coil in square meters
  • N is the number of turns of wire in the coil
  • H is the RMS magnetic field in amperes per meter.
  • Thearea of the antenna may be calculated knowing the diameter D (A 1rD /4) and since there may be many layers wound around the core 57, D is taken to be the mean diameter. Associated with the winding is a distributed capacitance whose capacitive reactance increases with increasing frequency while inductive reactance decreases with increasing frequency. When the inductive and capacitive reactances are equal at a particular frequency, the loop antenna is self resonant and the particular frequency is herein termed the self resonant frequency fr.
  • the curve of FIG. 5 is the output voltage vs. frequency characteristic, for a given magnetic field H of 1 amp per meter with 800 turns of wire, an area of 0.69 square meters and a core of free space.
  • the curve illustrates that the loop terminal voltage increases linearly to a peak point 60 and thereafter decreases linearly. Peak point 60 occurs at the self resonant frequency fr.
  • the linear response is approximately 6 db per octave, that is, for each doubling of the frequency the terminal voltage doubles.
  • the resonant frequency for the loop antenna of FIG. 3 is designed to occur above the band of frequencies being transmitted. In this manner the antenna is operated in the linear range 62 encompassing the voice band transmission. Accordingly, as the higher frequencies result in lower field strengths and as the loop antenna provides a higher output voltage for these frequencies the combined action being illustrated in FIG. 6 results in a terminal voltage which does not vary greatly with frequency within the band of interest.
  • curve 65 represents the magnetic field strength response such as previously illustrated in FIG. 4 and curve 66 represents the linear portion of the receiving loop response curve of FIG. 5. If the two curves are multiplied by one another (or added logarithmically), that is if, for each frequency, the actual value of H be utilized in equation (1), there results a substantially constant output voltage as illustrated by curve 68. It is to be noted that the transmitted audio signal is actually varying in amplitude; the voltage referred to is the RMS voltage. The amplification of the signal represented by curve 68 which is substantially linear in response to the receipt of the band of frequencies being transmitted insures a substantially distortionless output from the audio amplifier 40, FIG. 3, and an intelligible output signal from the output transducer 49.
  • Intelligible communications for a system is a necessity, particularly in a mine disaster situation since its use may be by injured, frightened, or confused personnel who must respond to given instructions. Because of transmitter power limitations in the mine and strong atmospheric noise levels at the surface, the available signal to noise ratios at the surface will be far less than those obtained with the transmission from the surface to the mine. However by using a narrow band code system with a low data rate as a miner response unit, the signal to noise ratio can be made sufficiently high to obtain reliable message transmission. These response units may be placed within refuge chambers with each being assigned a slightly different frequency from the others for identification purposes.
  • a seismic response may be made in accordance with received instructions by hammering on the mine wall or other mine structure.
  • FIG. 7 is a plan view of a long wire antenna 72 of length L, illustrating an approximate area of coverage 74 and FIG. 8 is a side elevational view illustrating the area of coverage 76 penetrating into the earth.
  • the coverage obtained with the system is dependent upon various factors such as earth conductivity, the length L of the wire antenna and the current coupled into it from the audio amplifier. In order to increase the coverage an arrangement such as illustrated in FIG. 9 may be utilized.
  • FIG. 9 there is provided a coupling means 80 for coupling the output of the audio frequency power amplifier to a plurality of antennas 83 and 84.
  • a plurality of audio frequency power amplifiers could be coupled to the microphone to drive respective antennas.
  • the coupling means of FIG. 9 as well as other coupling means, to be described, could incorporate the multiple tap arrangement of FIG. 2.
  • FIGS. 10 and 11 Other predetermined antenna placements are illustrated in FIGS. 10 and 11, FIG. 10 showing a'crossed pair, and FIG. 11 showing a radial array, by way of example.
  • FIG. 12 illustrates an alternative to the long wire antenna grounded at both ends, as previously described.
  • Coupling means 86 couples the output of the audio frequency power amplifier to a large loop antenna 89 which may, in a practical embodiment, have sides which are many thousands of feet in length.
  • the simplicity of the system, and particularly the receiver means minimizes expense such that each miner may be provided with the receiver means. Fabrication may be made utilizing integrated circuits and the receiver means may be easily carried on the miner or may be built into the miners helmet as illustrated in FIG. 13.
  • the helmet 92 carries a miners light 93 operated by a miner-carried battery 95.
  • a receiving loop antenna may be positioned conveniently on the miner or, as illustrated by numeral 98, may be positioned around the inside of the helmet 92 and an output speaker or earphones may be positioned on the brim 102 of the helmet 92.
  • the remainder of the receiving means is contained in a package 104 also mounted on the brim 102. Obviously the small size of the package 104 permits its placement in any other desired position on his helmet 92 or elsewhere on his person.
  • the present invention provides a voice communication link not only from the surface to the mine but additionally from the mine to the surface.
  • a transmitter means such as illustrated in FIG. 2 may be placed within the mine with the antenna ends grounded in the mine, and a receiver such as illustrated in FIG. 3 may be utilized at the surface. Since power requirements need not be kept'to a minimum at the surface, the receiving means may be operated at increased power levels to insure higher signal to noise ratios.
  • the transmitting antenna could also be of the type illustrated in FIG. 12 wherein the loop could be positioned around the walls of a tunnel.
  • the transmitter and receiver means are for spaced apart operation with at least one being for location within the earth.
  • a transmitter means includes an audio frequency power amplifier 112 receiving signals from an input means 115 which may be a microphone for real time voice transmissions or a recorded message to be transmitted, via a long wire antenna 118 buried beside, or as illustrated in FIG. 14, buried beneath a roadbed 120.
  • the transmitter means 110 includes the power supply 122, preamplifier 123, and the coupling means 125, as previously described.
  • a vehicle such as car 129 includes a receiving means 132 having a loop antenna 133 the receiving means being of the type described with respect to FIG. 3.
  • the vehicle thus could receive information or warnings from such transmissions which could for example, upon approaching an intersection or road hazard, warn the driver of the approaching hazard and the action he should be prepared to take.
  • FIG. 14 shows the designed output voltage versus frequency characteristic for the loop antenna 133.
  • the antenna is designed such that the response is relatively flat in the vicinity of the self resonant frequency fr and the self resonant frequency is within the band of frequencies being transmitted. This may be accomplished by adding resistance to the loop antenna to lower its Q thereby flattening the curve.
  • the self resonant frequency fr may be shifted downward by the addition of capacitance to the loopantenna such as across the loop antenna terminals.
  • operation of the loop antenna 133 is within the range from point 135 to point 136. Since the field strength will be relatively constant for the band of frequencies transmitted, the relatively constant portion of the loop response curve will result in a substantially constant output RMS voltage as heretofore described.
  • a communications system comprising:
  • said transmitter and receiver means being for spaced apart operation with at least one being for location within the earth;
  • said receiver means including:
  • ii means for connecting said audio amplifier to a source of operating potential
  • output transducer means for converting the output signal of said audio amplifier to an audible signal
  • said loop antenna having an increasing output voltage vs. frequency characteristic, for a given magnetic field, said characteristic being linear up to a self resonant frequency, after which said output voltage vs. frequency characteristic decreases;
  • said loop antenna being of a design that said self resonant frequency is above said band of frequencies being transmitted.
  • said transmitter means includes: 7
  • said antenna means is a relatively large loop.
  • said coupling means includes a transformer having a primary and a secondary winding
  • said antenna means includes a first and second long insulated wire sections connected to said secondary winding.
  • said coupling means includes a transformer having a primary and a secondary winding
  • said antenna means is a long insulated wire connected tov one end of said secondary winding, the other end ofsaid secondary winding being for connection to the earth.
  • said coupling means includes:
  • said secondary winding including multiple taps
  • said transmitter means includes:
  • said antennas being arranged'in a predetermined pattern in accordance with a desired area coverage.
  • a system according to claim l 'for mine use which includes:
  • Receiver apparatus for receiving through the earth transmission of an audio signal of a band of frequencies within the audio range, comprising:
  • said loop antenna having an increasing output voltage vs. frequency characteristic, for a given magnetic field, said characteristic being linear up to a self resonant frequency, after which said output voltage vs. frequency characteristic decreases;
  • said loop antenna being of a design that said self resonant frequency isabove said band of frequencies being transmitted;

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Details Of Aerials (AREA)
  • Near-Field Transmission Systems (AREA)
  • Transmitters (AREA)
US00106034A 1971-01-13 1971-01-13 Inductive loop through-the-earth communication system Expired - Lifetime US3740488A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US10603471A 1971-01-13 1971-01-13

Publications (1)

Publication Number Publication Date
US3740488A true US3740488A (en) 1973-06-19

Family

ID=22309114

Family Applications (1)

Application Number Title Priority Date Filing Date
US00106034A Expired - Lifetime US3740488A (en) 1971-01-13 1971-01-13 Inductive loop through-the-earth communication system

Country Status (8)

Country Link
US (1) US3740488A (fr)
AU (1) AU3736171A (fr)
BE (1) BE777931A (fr)
CA (1) CA941308A (fr)
DE (1) DE2200784A1 (fr)
FR (1) FR2121778B1 (fr)
GB (1) GB1382257A (fr)
ZA (1) ZA718534B (fr)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3411478A1 (de) * 1983-03-28 1984-10-04 Institut Français du Pétrole, Rueil-Malmaison, Hauts-de-Seine Verfahren zum uebertragen eines signals ohne elektrische verbindung durch eine leitende wand, insbesondere den rumpf eines seefahrzeugs und vorrichtung zu seiner durchfuehrung
US4652857A (en) * 1983-04-29 1987-03-24 Meiksin Zvi H Method and apparatus for transmitting wide-bandwidth frequency signals from mines and other power restricted environments
US4864301A (en) * 1987-07-24 1989-09-05 Richard J. Helferich Variable speed transmission recording and retrieval of data
US4905003A (en) * 1987-07-24 1990-02-27 Richard J. Helferich Analog/digital data storage system
US5003576A (en) * 1987-07-24 1991-03-26 Richard J. Helferich Analog/digital voice storage cellular telephone
USRE34976E (en) * 1987-07-24 1995-06-20 Richard J. Helferich Analog/digital voice storage cellular telephone
USRE37618E1 (en) * 1987-07-24 2002-04-02 Richard J. Helferich Analog/digital data storage system
US20100311325A1 (en) * 2009-06-03 2010-12-09 Marshall Radio Telemetry, Inc. Systems and methods for through-the-earth communications
US20120293150A1 (en) * 2008-03-28 2012-11-22 Broadcom Corporation IC Package with Embedded Transformer
US20130003244A1 (en) * 2007-12-12 2013-01-03 Broadcom Corporation Integrated Circuit Package with Transformer
US8395878B2 (en) 2006-04-28 2013-03-12 Orica Explosives Technology Pty Ltd Methods of controlling components of blasting apparatuses, blasting apparatuses, and components thereof

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2163029B (en) * 1984-08-06 1987-11-18 Peter James Raynor Inductive communication system
GB8530772D0 (en) * 1985-12-13 1986-01-22 Gradwell Paul Stephen Communication system
CA1311527C (fr) * 1988-05-02 1992-12-15 Kenneth E. Hjelmstad Systeme d'alarme-incendie electromagnetique pour mine souterraine
ES2330286B1 (es) * 2007-07-26 2010-09-21 Universidad De Zaragoza Metodo y dispositivo de transmision y recepcion de audio para comunicaciones bidireccionales mediante inyeccion de corriente.
GB2563872B (en) 2017-06-28 2022-06-15 Kirintec Ltd Communications system

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1015485B (de) * 1956-07-21 1957-09-12 Siemens Ag Bewegliche Mikrophonanordnung mit einem Mikrophonverstaerker, der insbesondere mit dem Mikrophon eine Baueinheit bildet
US2853557A (en) * 1955-01-28 1958-09-23 Dictograph Products Co Inc Sound distribution system
US2980793A (en) * 1956-06-11 1961-04-18 Electronic Safety Engineering Restricted range radio transmitting system
GB1031994A (en) * 1965-01-22 1966-06-08 John Davis & Son Derby Ltd Improvements in inductive signalling systems for mines, tunnels and similar situations
US3323063A (en) * 1964-08-07 1967-05-30 Theodore Granik System for re-diffusion of received radio signals
US3470474A (en) * 1966-12-23 1969-09-30 Donald E Bilger Underground radio communication system for highways
US3495209A (en) * 1968-11-13 1970-02-10 Marguerite Curtice Underwater communications system

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2853557A (en) * 1955-01-28 1958-09-23 Dictograph Products Co Inc Sound distribution system
US2980793A (en) * 1956-06-11 1961-04-18 Electronic Safety Engineering Restricted range radio transmitting system
DE1015485B (de) * 1956-07-21 1957-09-12 Siemens Ag Bewegliche Mikrophonanordnung mit einem Mikrophonverstaerker, der insbesondere mit dem Mikrophon eine Baueinheit bildet
US3323063A (en) * 1964-08-07 1967-05-30 Theodore Granik System for re-diffusion of received radio signals
GB1031994A (en) * 1965-01-22 1966-06-08 John Davis & Son Derby Ltd Improvements in inductive signalling systems for mines, tunnels and similar situations
US3470474A (en) * 1966-12-23 1969-09-30 Donald E Bilger Underground radio communication system for highways
US3495209A (en) * 1968-11-13 1970-02-10 Marguerite Curtice Underwater communications system

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3411478A1 (de) * 1983-03-28 1984-10-04 Institut Français du Pétrole, Rueil-Malmaison, Hauts-de-Seine Verfahren zum uebertragen eines signals ohne elektrische verbindung durch eine leitende wand, insbesondere den rumpf eines seefahrzeugs und vorrichtung zu seiner durchfuehrung
US4652857A (en) * 1983-04-29 1987-03-24 Meiksin Zvi H Method and apparatus for transmitting wide-bandwidth frequency signals from mines and other power restricted environments
USRE37618E1 (en) * 1987-07-24 2002-04-02 Richard J. Helferich Analog/digital data storage system
US4905003A (en) * 1987-07-24 1990-02-27 Richard J. Helferich Analog/digital data storage system
US5003576A (en) * 1987-07-24 1991-03-26 Richard J. Helferich Analog/digital voice storage cellular telephone
USRE34976E (en) * 1987-07-24 1995-06-20 Richard J. Helferich Analog/digital voice storage cellular telephone
US4864301A (en) * 1987-07-24 1989-09-05 Richard J. Helferich Variable speed transmission recording and retrieval of data
US8395878B2 (en) 2006-04-28 2013-03-12 Orica Explosives Technology Pty Ltd Methods of controlling components of blasting apparatuses, blasting apparatuses, and components thereof
US20130003244A1 (en) * 2007-12-12 2013-01-03 Broadcom Corporation Integrated Circuit Package with Transformer
US8855581B2 (en) * 2007-12-12 2014-10-07 Broadcom Corporation Integrated circuit package with transformer
US20120293150A1 (en) * 2008-03-28 2012-11-22 Broadcom Corporation IC Package with Embedded Transformer
US8912639B2 (en) * 2008-03-28 2014-12-16 Broadcom Corporation IC package with embedded transformer
US20100311325A1 (en) * 2009-06-03 2010-12-09 Marshall Radio Telemetry, Inc. Systems and methods for through-the-earth communications

Also Published As

Publication number Publication date
AU3736171A (en) 1973-06-28
BE777931A (fr) 1972-07-12
GB1382257A (en) 1975-01-29
DE2200784A1 (de) 1972-07-20
CA941308A (en) 1974-02-05
FR2121778A1 (fr) 1972-08-25
FR2121778B1 (fr) 1974-11-08
ZA718534B (en) 1972-09-27

Similar Documents

Publication Publication Date Title
US3740488A (en) Inductive loop through-the-earth communication system
US5301082A (en) Current limiter circuit
US5093929A (en) Medium frequency mine communication system
US3609247A (en) Inductive carrier communication systems
US6195561B1 (en) Antenna system for two-way UHF underground radio system
Murphy et al. Underground mine communications
US4507646A (en) Radio communication system
GB2126845A (en) Radio communication systems for underground mines
US3760278A (en) Limited range radiocommunication system
Monk et al. Communication with moving trains in tunnels
JPS63500909A (ja) ロ−プによって情報伝達するケ−ブルカ−
US1220005A (en) Wireless signaling system.
US3191122A (en) Communication system for sielded areas
US2427979A (en) Communication and control system for airplanes
US2257094A (en) High frequency radio relay system
WO1997027645A1 (fr) Systeme de communication electromagnetique basse frequence et son antenne
US3715664A (en) Method of repeating rf-borne signal across an earth barrier
JPS5842329A (ja) 映像伝送装置
US1375675A (en) Signaling method and system
Ilsley et al. Experiments in underground communication through earth strata
US5669065A (en) Completely redundant communication system utilizing radiating transmission line
CN220067424U (zh) 一种跨介质磁通讯系统
CN203335133U (zh) 井下音频广播报警装置
Chufo Vehicular communications 2500 feet underground
Coggeshall et al. Some Studies on Emergency Mine Communications